It's not overstimulation, it's understimulation. Everything else is always more interesting than the thing you're currently doing. That link is more interesting than the tab I'm looking at, and now I have 279 (at the time of writing) tabs open. That hobby is more interesting than what I'm doing, and now have have 30 hobbies and suck at all of them. I have something important tomorrow, but there's 100 things more interesting right now. I get bored after approximately ten seconds.
Normal people get bored and distracted too, but the difference is this is chronic and is always on and can cause incredibly absurd or at least interesting results over the long term. If there's a way to get stimulation, adhd people will try it. For example: complex music (ie. breakcore, dnb, psytrance), strong food flavors, doing random bullshit and seeing what happens, and maybe some masochistic tendancies. But once it becomes the new normal, it doesn't work as well; the default is to be understimulated.
The task of focusing on things is like a solid brick wall, but mental instead of physical. Some people don't think it exists, or that I'm making it up. People who do want to help usually can't, since they don't really understand having adhd. Useless advice is ubiquitous: "That solid brick wall doesn't really exist!" or "Use your inner strength to break through the solid brick wall!" or "I did xyz to reach my goal behind this distinct lack of solid brick wall!" or "Just do the thing lol".
Some people like natural methods to help with it, such as exercise or meditation. It's certainly possible to scale the solid brick wall, and get better at it over time. However, I'd rather take the easy way out and take what's effectively a magical pill that removes this pain from my life (adderall). I'm still not sure if adhd has any nice benefit, or if its a completely waste of time; "hyperfocus" is nice, but honestly I'd rather be able to focus normally so I don't lose track of time.
At this point, it's probably a good idea to declare attention bankrupcy and close every tab and start fresh. I probably won't though, since I don't like closing unread tabs.
When focus is precious and slippery, willpower and energy become rare and valuable resources.
Some other neat side effects